Abstract
Many animals partition resources to avoid competition, and in colonially-breeding species this often leads to divergent space or habitat use. During the non-breeding season, foraging constraints are relaxed, yet the patterns and drivers of segregation both between and within populations are poorly understood. We modelled habitat preference to examine how extrinsic (habitat availability and intra-specific competition) and intrinsic factors (population, sex and breeding outcome) influence the distributions of non-breeding grey-headed albatrosses Thalassarche chrysostoma tracked from two major populations, South Georgia (Atlantic Ocean) and the Prince Edward Islands (Indian Ocean). Spatial segregation was greater than expected, reflecting distinct seasonal differences in habitat selection and accessibility, and avoidance of intra-specific competition with local breeders. Previously failed birds segregated spatially from successful birds during summer, when they used less productive waters, suggesting a link between breeding outcome and subsequent habitat selection. In contrast, we found weak evidence of sexual segregation, which did not reflect a difference in habitat use. Our results indicate that the large-scale spatial structuring of albatross distributions results from interactions between extrinsic and intrinsic factors, with important implications for population dynamics. As habitat preferences differed substantially between colonies, populations should be considered independently when identifying critical areas for protection.
Highlights
Partitioning of resources between ecologically-similar animals promotes their coexistence, and often involves the use of different areas or habitats[1,2]
The successful breeders were tracked for 490 ± 78 days, covering the whole non-breeding period for all but three birds with logger batteries that failed before retrieval
We found no evidence of sexual segregation across the whole utilization distributions; we did find males and females from South Georgia (SG) segregated in their core (50%) but not general use (90%) distributions during summer only (Supplementary Table S2, Fig. S5)
Summary
Partitioning of resources between ecologically-similar animals promotes their coexistence, and often involves the use of different areas or habitats[1,2]. In a pioneering tracking study, GHA from South Georgia exhibited a diversity of migration strategies; some remained resident in the southwest Atlantic, whereas others travelled to the southwest Indian Ocean, or undertook one or more circumpolar trips during a single non-breeding period[11]. As such, they are an excellent model species for investigating large-scale space use of animals over time. The non-breeding distributions of other populations are so far unknown, as are the movements of failed birds
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